Many electronic components can function properly when the operating temperature is within a specified temperature range. In particular, it is desirable to keep the operating temperature of these electronic components below a maximum temperature limit. The excessive thermal energy associated with the temperature above the maximum limit may degrade the performance and lifetime, and cause malfunction or even permanently damage in these components. Unfortunately, most electronic components internally generate heat by converting electrical energy into thermal energy due to the inherent electrical resistance. Therefore, it is often necessary to implement some cooling mechanism to properly dissipate the heat in electronic circuits and devices.
Heat dissipation is particularly important in devices such as computers that have high-density electronic components formed one or more integrated circuit boards. Heat sinks and fans have been widely used as cooling devices in many circuit board designs. A heat sink is usually attached to a heat-generating component such as a microprocessor chip to remove the heat and then the heat is further dissipated away from the circuit board by forced air circulation by using a fan.
FIG. 1 illustrates an example of a conventional printed circuit board with a heat sink and a fan formed over a heat-generating integrated circuit on a motherboard. The heat-generating integrated circuit and other components are formed on the same motherboard.
However, heat sinks and fans are usually bulky and increase the dimension (e.g., height) of a circuit board. This limits the applications of heat sinks and fans, especially in compact devices such as portable computers and rack-mounted systems that have multiple circuit boards stack together. Many cooling fans such as miniature fans commonly installed in personal computers are prone to failure due to their typical operating conditions such as elevated temperatures, pressure drop across the fan, and adverse effects of the particles in the ambient air.
Other alternative cooling techniques have been used in integrate circuit devices, including heat pipes, thermoelectric coolers, and liquid cooling. But these techniques are also limited due to cost, complexity, reliability and cooling efficiency.
The present disclosure provides techniques and electronic devices to cool printed circuit boards without conventional heat sinks and fans. At least two circuit boards are used to separate one or more heat-generating circuit elements from other circuit elements. An electrically-insulating thermal conductor is used to dissipate the heat in the ambient air outside the circuit boards and prevents the heat from dissipating into the air near the circuit components.
One embodiment of such an electronic device includes a first printed circuit board having a ground conducting layer that is connected to a metal chassis and a circuit surface configured to support circuit elements, and a second printed circuit board electrically connected to the first printed circuit board and having a circuit surface that supports a heat-generating circuit element. The heat-generating circuit element generates more heat than any of the circuit elements on the first printed circuit board. The second printed circuit board is disposed relative to the first printed circuit board in such a way that said circuit surface of the second printed circuit board opposes the circuit surface of the first printed board.
An electrically insulating thermal conductor medium is formed between the first and second circuit boards. One side of the thermal conductor medium is in direct contact with the heat-generating circuit element and another side of the thermal conductor medium is in thermal contact with the ground conducting layer in the first circuit board so that the heat from the heat-generating circuit element can be at least partially dissipated to the metal chassis.
The thermal contact between the thermal conductor medium and the ground conducting layer is formed by an electrically conducting layer disposed on the circuit side of the first printed circuit board. A plurality of electrical conductors disposed to connect the conducting layer in order to transfer thermal energy from the thermal conductor medium to the ground layer.
An output panel of the first circuit board may also be in thermal contact with the thermal conductor medium to further dissipate the heat into the ambient air.
One advantage of the above device is that fans and conventional heat sinks are eliminated so that the device can be made more compact and reliable.
These and other aspects and associated advantages of the present invention will become more apparent in light of the following detailed description, the accompanying drawings, and the claims.